In recent years, along with rapid proliferation of mobile electronic devices such as digital cameras, smartphones, and tablets, increasing are the demand for power storage devices such as secondary batteries which are used as power sources of these devices and can be repeatedly used by charging, and the demand for the increase of their capacity and energy density.
These power storage devices commonly include a solution of an electrolytic salt in an aprotic organic solvent as an electrolytic solution. Various combination of these electrolyte salts and aprotic organic solvents have been studied up to date. Examples of the widely used electrolytic salts include quaternary ammonium salts (Patent Documents 1 to 3) and quaternary phosphonium salts (Patent Document 4), owing to their high solubility in organic solvents and degree of dissociation, and wide electrochemical stable ranges.
However, these electrolytic salts contain halogen atoms such as fluorine atoms in anions, and thus still have problems in terms of environment load, so that these problems are expected to be solved. Additionally, the electrolytic salts for the above-described uses are demanded to have electrochemical properties such as high ion electrical conductivity and wide electric potential windows.